Roasting pryites fines



Jan. 2, 1934. R. F. BACON Er Al.

ROASTING PYRITEs FINES Filed Nov. l21, 19:51.

Patented Jan. 2, 1934 ROASTING PYRITES FINES Raymond F. Bacon,Bronxville, N. Y., and Wilber Judson, Newgulf, Tex.

Application November 21, 1931 Serial No. 576,492

7 Claims.

In the suspension or flash roasting of pyritesnes as ordinarilyconducted, numerous operatving dimculties have presented themselveswhich are distinctly detrimental to the effective conduct of theroasting operation. Principal among these are the formation of sinteredaccretions upon the walls of the roasting furnace, incompletedesulphurization of the pyrites, and the too rapid burning out of Vthefurnace. The formation of accretions is of quite common occurrence andis particularly objectionable, for the accretions assume suchsubstantial and obstructing proportions in a short time that theoperation of the furnace must be suspended at all too frequent intervalsto permit their being broken away from the furnace walls. This breakingaway of the large masses of accretion, moreover, involves considerablewear and tear upon the furnace, and in addition results in the waste ofmaterial amounts of green or undesulphurized pyrites which is frequentlyenclosed in the accretions. Our investigations of this problem indicatethat 30 the objectionable accretions resulting from sintering, theincomplete desulphurization attendant thereupon, the rapid burning outof the furnace, and in some cases slagging of the furnace lining withthe oxidized pyrites, are in large part ascrib- 5 able to theexcessively high temperature which results in the usual flash roasting.

Pyrites is highly combustible 'even in lump form, and with the largesurface area presented to the oxidizing gas in the suspension or ashroasting of nes, the oxidation, with its accompanying production ofheat, proceeds with such intensity and rapidity that a very high localtemperature results. As a consequence of this excessively 'hightemperature, which because of the intensity and rapidity of the actioncannot be controlled by ordinary means, there will be a natural tendencyto burn out the furnace relatively quickly, and material quantities ofthel pyrites will be sintered and form accretions upon the Walls beforecomplete desulphurization has taken place.

In accordance with our invention, the aforenoted difficulties areovercome and a highly effective andeconomical process is provided by rstheating the suspended fines in a relatively nonoxidizing atmosphere todrive off the volatile sulphur atom, then roasting the residualsulphide, which for practical purposes can be designated as ironmonosulphide, by suspension in` an oxidizing gas, and utilizing the hotgases from the o0 roasting of the monosulphide as a hot gaseoussuspending medium to drive off the volatile sulphur from fresh portionsof the pyrites.

In the accompanying drawing an illustrative arrangement of apparatus isshown more or less schematically by means of which the process of ourinvention may be carried out.

Reference numeral 1 designates the distillation chamber constructed ofrebrick or the like, into which pyrites fines or flotation concentratesfrom the hopper 2 are introduced through the mediumof the screw conveyor3 leading to the inlet duct 4. The hot sulphur dioxide gases from theroasting chamber 5 to be hereinafter described, are introduced into thechamber 1 through tuyres 6 and 7 leading from feed pipes 8 and 9respectively, which pipes are connected to the exit duct 10 from theroasting chamber 5.

A damper or other valve 11 is disposed. in the duct 10 to p ermit thecutting in or out of the 80 upper tuyres 7, and suitable valves 12 maybe disposed in the tuyres and other ducts as necessary or desirable. Thedischarge gases from the distillation chamber pass off through a housingor preheating chamber 13 surrounding the pyrites inlet duct 4 and thencethrough the exit duct 14. The iron monosulphide resulting from thedistillation operation passes downwardly through a grate 15 into thescrew conveyor 16 and is conveyed to the inlet duct 17 of the roastingcham- 90 ber 5.

Air or oxygen, preheated or not as desired, is blown in at the bottom ofthe roasting chamber through the tuyres 18 and passes upwardly incountercurrent flow with the monosulphide showering down from the inletduct 17. The discharge gases from the roasting chamber pass olf throughthe exit duct 10 leading to the distillation chamber 1. The iron oxideproduced in the roasting chamber passes through the grate 19 100 to thescrew conveyor 20 leading to the cinder outlet 21. The roasting chamber,as is the distillation chamber, is constructed of f'lrebrick or othersuitable non-corrodible refractory material of suitable insulatingthickness, and the various ducts, pipes, etc. are preferably providedwith suitable insulation to retain -the heat in the gases passingtherethrough.

An illustrative method of operation is as follows: In one mode ofinitiating the operation, the roasting chamber 5 is strongly preheated,for example by means of oil burners inserted through suitable work-holesin the chamber, until its temperature is above the ignition point ofpyrites, for example approximately 850 C. An adequate quantity of thefines is then admitted to the roasting chamber either by way of thedistillation chamber 1 and the screw conveyor 16, ordirectly thereintowith suitable provision therefor, and air is blown at a suitablevelocity through the tuyres 18. Contacting with the pyrites the air willserve to rapidly oxidize the same to iron oxide and sulphur dioxide withthe liberation of a very substantial amount of heat. The hot gasesresulting from this initial roasting, containing principally sulphurdioxide and nitrogen, pass off through the exit duct 10.

and thence through the feed pipes 8, 9 and the tuyres 6, 'l respectivelyinto the distillation chamber 1.

When the distillation chamber has been heated to a suitable degree bythe passage of these hot gases, which heating may be supplemented orreplaced by a preliminary preheating with oil burners as in the roastingchamber, and a fairly steady current of hot gas is passing through thechamber, the flow of pyrites is started from the hopper 2 by the screwconveyor 3. Showering downwardly through the inlet duct 4 the pyrites ispreheated in its passage therethrough by heatexchange with the hot gasespassing off through the housing 13, and entering the distillationchamber, it is subjected to the further action of .the hot gases thereinto volatilize the feeble sulphur atom. To obtain satisfactory results inthis respect, it is desirable that the pyrites be heated to atemperature not substantially less than 500 C., at and above which pointthe volatile sulphur will distill off in a satisfactory fashion. Thetemperature of the pyrites should not however, be elevated to a point(approximately 850 and above)Y where sintering might take place. Ahighly favorable distillation temperature is readily maintainable by thehot gases from the roasting chamber which can be supplied attemperatures of 800-1000 C. and above with little difficulty. The rateof flow of the pyrites and the hot gases, the length of the distillationchamber, etc., should be so regulated that the pyrites is maintained incontact with the hot gases for a sufficient period of time to result insubstantially all of the feeble sulphur atom being driven 011'. Y

The partially desulphurized pyrites, which for convenience we will referto as the monosulphide, passes through the grate 15 and is delivered bythe screw conveyor 16 to the inlet duct 17 to the roasting chamber. Thegrate 15 will serve to retain any agglomerations too large forconvenient handling by the conveyor which might have been formed in thedistillation chamber, and these may be broken up by access through asuitable work-holewhen and if they have accumulated to a suiicientextent to warrant such a procedure.

The hot monosulphide, which will beat a temperature in the approximateneighborhood of 500 or thereabove, showers down into the hot roastingchamber 5 where it comes in contact with the countercurrent of airflowing in through the tuyres- 18. The flow of air with respect to thepyritesl` is preferably so regulated that substantially the theoreticalamount of oxygen for complete desulphurization of the sulphide issupplied to the chamber and, if desired, the air may b'e preheated. Suchcan be conveniently accomplished by heat-exchange with the hot exitgases from the distillation chamber.

An intense oxidation of the monosulphide will take place in the roastingchamber, and due to the condition to which the pyrites has been reduced,much less tendency towards sintering and the formation of accretions isexhibited. The conduct of the roasting operation and the resultingtemperature in the roasting chamber should be so regulated however, thatthe temperature invthe upper portion of the chamber wherein theATsulphide is principally in the state of monosulphide, should notexceed the fusing temperature of thcmonosulphide (approximately S50-900C.) This/can be readily'accomplished by providing a chamber of suitablelength, regulating the rate of feed orf the sulphide and air, etc., aswill be apparent to one skilled in the art. As the lower zones in theroasting chamber are approached it appears to be possible to carry thetemperature up to a much higher degree without producing sintering. Thisseems to be due to the fact thatwhen aquantity of FezOa is present thetendency toward sintering of the monosulphide, or whatever theparticular composition of the sinterable sulphide may be, isconsiderably inhibited. As a consequence, in the lower portions of theroasting chamber the temperatures may be elevatedl as high as 1400 C.without sintering, and this is of advantage for it permits a verythorough desulphurization of the ore before discharge.

In its passage through the roasting chamber the monosulphide isconverted to sulphur dioxide and iron oxide, either as FeaOs and/orFeaOi depending upon the conditions of the operation, and the roastingshould be so controlled, by proper regulation nof the length and designof the chamber, temperatures, rate of flow of the air and ore, and thelike, that the sulphide will be suspended under favorable conditions fora suincient period of time to assure the substantially completeoxidation of the sulphide by the oxygen in the air.

The particles of iron oxide cinder from the roasting chamber passthrough the grate 19 into the screw conveyor 20 whence they aredischarged through the cinder outlet 2l. The hot roaster gases,containing principally sulphur dioxide and nitrogen, together with someslight amount of oxygen which is generally not present in sulcientquantity to exhibit any appreciable oxidation effect in the distillationchamber, pass up- I wardly through the exit duct 10 for introductioninto the distillation chamber.

The temperature of these gases will generally be in the neighborhood of800-1000 C. and above. Passing from the exit duct 10 into the feed pipe8, which surrounds the distillation chamber 1, the hot gases'areintroduced into the chamber through the tuyres 6 which are providedaround the chamber in any desired number. The rate of flow through, oroperation of, each tuyre can be controlled by a suitable valve 12. It isdesirable that the hot gases be introduced into the distillation chamberat points above the bottom tuyres 6 in order to provide a more or lessuniform temperature throughout the chamber, with resultant facilitationof the distillation. To this end a second series of tuyres '7 leadingfrom the feed pipe 9 are disposed in a higher zone of the distillationchamber and, if desired, supplementary sets of tuyres may be provided atadditional points. The operation of these supplementary sets of tuyresmay be controlled by the medium of dampers such as 1l, as supplementedor displaced by the individual tuyre valves 12.

The hot gases introduced through the tuyres will pass upwardly throughthe chamber 1 in countercurrent flow to the pyrites being introducedthrough the duct 4, accomplishing the distillation of the volatilesulphur atom of the pyrites in passage, and pass oi by way of thehousing 13 through the exit duct 14. These gases will lconsist ofsulphur dioxide, elemental sulphur, nitrogen, and some small amount ofoxygen in relatively inactive concentration. The gases are quite hot,for example 400 or above, and as has been noted, they can if desired beutilized as a sole or partial source of heat for preheatlng the airbeing introduced into the roasting chamber.

Due to the fact that a lines roasting is involved, these exit gases willalso carry entrained therein some amount of dust which it is preferableto remove prior to any subsequent treatment or use of the gases. Thismay be accomplished by passing the gases as necesssary through one or aseries of dust chambers of any suitable type, such for example asmechanical baille chambers, electrostatic precipitation chambers, or acombination of both. After the removal of the dust the gases may then betreated or utilized as desired.

In view of the fact that these gases already contain a substantialquantity of elemental sulphur, are quite rich in sulphur dioxide, andare substantially free from oxygen, they are admirably adapted fortreatment to recover elemental sulphur. This can be accomplished, forexample, by reaction of the sulphur dioxide in the gases withcarbonaceous reducing agents such as producer gas, water gas, naturalgas, solid carbon, and the like, or with hydrogen sulphide, or in anyother suitable manner. elemental sulphur already present in the gasesmay/be removed therefrom by condensation, as for example by means of awaste heat boiler, prior to any treatment of the sulphur dioxide ifsuchr preliminary removal is of advantage, or if the presence of theelemental sulphur is not particularly detrimental, it may be permittedto remain in the gases and the total sulphur subsequently collected inone operation.

Apart from the particular adaptability of these gases for elementalsulphur recovery, they may likewise be advantageously utilized for theirsulphur dioxide, for example, in the manufacture of sulphuric acid.Despite the fact that they contain a substantial amount of the sulphurin elemental form, they are, nevertheless, as a result of the thoroughdesulphurization attainable by the roasting process of our invention,quite rich in sulphur dioxide. The latter is generally present inamounts ranging from 10-13%, a content when diluted with air quitesuitable for sulphuric acid manufacture. Moreover, if it is desired toincrease the sulphur dioxide concentration, the elemental sulphurpresent in the gases can be readily burned thereto to the extentdesired, and any residual sulphur removed. By burning the entire sulphurcontent of the gases it is possible to produce a gas containing as highas 1215% sulphur dioxide.

The foregoing description is intended merely to be illustrative andvarious changes may be made in the operation and apparatus as will beapparent to one skilled in the art. In the apparatus, for example, thedistillation chamber and the roasting chamber may be disposed upon thesame level instead of as shown. Such an arrangement will necessitate theprovision of a They suitable elevator to convey the sulphide from thebottom of the distillation chamber to the top of the roasting chamber,and under some circumstances it may be found necessary to supplement theaction of the blower at the tuyres of the roasting chamber by theinclusion of a suction fan or a blower either at the exit end of thedistillation chamber or between the roasting chamber and distillationchamber, or elsewhere in the system, to assist the downward ilow of theexit gas from the top of the roasting chamber into the bottom of thedistillation chamber. Such supplemental suction fans or blowers can ofcourse be similarly included in the arrangement shown if their use isnecessary or desirable to control the ow of the gases through thatsystem.

Likewise, the screw conveyors shown for feeding solid material to thechambers may be replaced by other feeding means which will permitsuitable control of the rate of feed of the solid. If it is desired, asuitably insulated storage hopper provided with a regulatable gate atthe discharge end, may be inserted in advance of the roasting chamber toreceive the hot sulphide from the distillation chamber and feed it at acontrolled rate to the roasting chamber.

The mode of operation is also susceptible to various modifications. Ininitiating the operation, for example, instead of roasting the rst partof the pyrites without a preliminary distillation of the feeble sulphuratom, the distillation chamber may be heated electrically, or in anyother suitable fashion, to bring about the distillation of the feeblesulphur from the initial charge of pyrites before its introduction intothe roasting chamber, and such auxiliary supply of heat may bemaintained until the operation is functioning properly and the hot gasesfrom the roasting chamber can be relied upon to provide the heatnecessary for the distillation. In preheating the air or otheroxygen-containing gas for the roasting operation, the hot cinder fromthe roasting chamber may be eiectively utilized as an alternative orsupplemental source of heat. This may be accomplished by simplyintroducing the air through the cinder outlet Where it will pass incontact with the hot cinder, or it may be passed in heat-exchangingrelationship with the hot cinder externally of the chamber and thenintroduced as shown.

While the foregoing detailed description is directed principally to ironpyrites fines, or notation concentrates, the operation is of courselikewise adapted for the treatment of nely divided marcasite,chalcopyrites, and other similar sulphide ores, all of which areintended to be included in the term pyrites fines used in the appendedclaims.

We claim:

1. In a process for treating pyrites-bearing material in which thematerial is heated to distill the volatile sulphur of the pyrites andproduce a gaseous product containing elemental sulphur vapor and toconvert the pyrites substantially to the monosulphide of iron, and themonosulphide of iron is roasted to produce a gaseous product containingsulphur dioxide, the improvement which comprises subjecting thepyrites-bearing material and the monosulphide of iron to thedistillation and roasting treatments while in gaseous suspension.

2. In a process for treating pyrites-bearing material in which thematerial is heated to distill the volatile sulphur of the pyrites andproduce a gaseous product containing elemental sulphur vapor and toconvert the pyrites substantially to the monosulphide of iron, and themonosulphide of iron is roasted to produce a gaseous product containingsulphur dioxide, the improvement which comprises subjecting themonosulphide of iron to the roasting treatment while in gaseoussuspension, and utilizing the heat generated in the roasting operationto distill the volatile sulphur of the pyrites.

3. In a process for treating pyrites-bearing material in which thematerial is heated to distill the volatile sulphur of the pyrites andproduce a gaseous product containing elemental sulphur vapor and toconvert the pyrites substantially to the monosulphide of iron, and themonosulphide of iron is roasted to produce a gaseous product containingsulphur dioxide, the improvement which comprises subjecting themonosulphide of iron 1o the roasting treatment while in gaseoussuspension, and passing the gaseous product of the roasting operation incontact with pyrites-bearing material in the distilling operation,thereby to utilize the heat generated in the roasting operation for thedistillation of the volatile sulphur of the pyrites.

4. In a process for treating pyrites-bearing material in which thematerial is heated to distill the volatile sulphur of the pyrites andproduce a gaseous product containing elemental sulphur vapor and toconvert the pyrites substantially to the monosulphide of iron, and themonosulphide of iron is roasted to produce a gaseous product containingsulphur dioxide, the improvement which comprises subjecting thepyritesbearing material to the distilla ion treatment while in gaseoussuspension, and utilizing the heat generated in the roasting operationto distill the volatile sulphur of the pyrites.

5. In a process for treating pyrites-bearing material in which thematerial is heated to distill the volatile sulphur of the pyrites andproduce afgaseous product containing elemental su!- phur vapor and toconvert the pyrites substantially to the monosulphide of iron, and themonosulphide of iron is roasted to produce a gaseous product containingsulphur dioxide, the improvement which comprises subjecting thepyritesbearing material to the distillation treatment while insuspension in the gaseous product of the roasting operation.

6. In a process for -treating pyrites-bearing material in which thematerial is heated to distill the volatile sulphur of the pyrites andproduce a gaseous product containing elemental sulphur vapor and toconvert the pyrites substantially to the monosulphide of iron, and themonosulphide oi' iron is roasted-tto produce a gaseous productcontaining sulphur dioxide, the improvement which comprises subjectingthe pyritesbearing material and the monosulphide of iron to thedistillation and roasting treatments while in gaseous suspension, andutilizing the heat generated in the roasting operation to distill thevolatile sulphur of the pyrites.

7. In a process for treating pyrites-bearing material in which thematerial is heated to distill lthe volatile sulphur of the pyrites andpro-` duce a gaseous product containing elemental sulphur vapor and toconvert the pyrites substanf tially to the monosulphide of iron, and themonosulphide of iron is roasted to produce a gaseous product conainingsulphur dioxide, the improvement which comprises subjecting thepyritesbearing material and the. monosulphide of iron to thedistillation and roasting treatments while in gaseous suspension, andutilizing the gaseous product oi the roasting operation to maintain thepyrites-bearing material in suspension and to provide heat fordistilling the volatile sulphur of the pyrites.

RAYMOND F. BACON.

WILBER JUDSON.

